There are a variety of treadmills on the market. One of the treadmills is a walking treadmill, which provides a flywheel to facilitate the running of the treadmill belt through the reverse thrust exerted by the user on the treadmill belt. The faster the speed of running, the faster the running speed of the runner. Because the flywheel has the gravitational acceleration of rotation, it is unable to stop the running of the treadmill belt quickly if the user wants to stop running. If the user stops running in a quick manner, he/she may have the risk of falling off the treadmill.
In order to solve the aforementioned problems, an electric treadmill is developed. The power of the existing electric treadmill adopts a single motor with a single steering as a power source for traction of the treadmill belt. The power source is a DC motor or an AC frequency conversion motor. However, it is well known that the range of the power provided by the DC motor is limited and it cannot be used indefinitely. Although the range of the power provided the AC frequency conversion motor is wide, the magnetic flux of the rotator is extremely saturated at a very low frequency (low speed). It is difficult to control the AC frequency conversion motor, and even there is the risk of burning. When the AC frequency conversion motor is used at a low frequency, the frequency convertor will automatically reduce the voltage acting on the motor, so that the torque will be reduced greatly. For the AC frequency conversion motor, a constant torque is applied to 120 HZ below, and a constant power is applied to 120 HZ above. Therefore, when the motor is running in the condition of more than 120 HZ high frequency, the motor cannot maintain a high level of torque output, so it limits the range of the power output.
As to the power source of the existing treadmill, no matter which is used (DC motor or AC frequency conversion motor), it is necessary to make a choice for the speed provided. For example, for the use of rehabilitation, the power source must be outputted at a very low speed. For the use of running, the power source must be outputted at a high speed. In order to reduce the restriction caused by the above situation, most of treadmills for rehabilitation adopt an AC frequency conversion motor having a wide range of output, such that it can meet the demands for rehabilitation at a very low speed and the demands for fitness and exercise at a high speed.
The aforesaid existing treadmill has to use a motor for driving the treadmill belt. A passive electric treadmill used for rehabilitation is developed accordingly. In fact, the walking treadmill is dangerous. The other electric treadmill is used for strengthening cardiopulmonary function only, and it must cooperate with a circuit board, a console and a motor so the relative cost is high. In view of the aforementioned defects, a magnetic treadmill is developed. The magnetic treadmill is provided with a magnetic wheel for damping control, but it cannot control the speed. Besides, it cannot be adjusted for training leg muscular endurance as desired according to the ability of the user. Accordingly, the inventor of the present invention has devoted himself based on his many years of practical experiences to solve these problems.